A transducer may here in particular be an actuator, a sensor or a generator, but the invention may also refer to other types of transducers.
Such a dielectric transducer structure is known from US 2004/0012301 A1. Dielectric transducers work by using the attraction between two electrodes located on an elastomeric body that leads to a compression of the body in one direction and a corresponding extension of the body in a second direction. If such structures are used as actuators, the electrostatic force between the two electrodes is used to compress the body. Alternatively, such structures may be used as sensors by operating the electrodes as the plates of a capacitor. In this mode an external force compresses the body in one direction and reduces the distance between the electrodes. Thus the capacity of the electrode capacitor is increased allowing to measure the applied force. According to US 2004/0012301 A1 at least one of the boundary surfaces has a waved area with heights and depths as extreme values running parallel to a transverse direction of the body. With this solution the transducer structure can be easily extended in one direction of the boundary surface. On the other hand, the transducer structure will display a very small compliance to elastic deformations in the direction transversal to the direction of corrugation.
WO 03/056287 A1 shows another dielectric transducer structure. In this case two elastic bodies with one flat and one corrugated surface each are laminated together with their flat surfaces facing each other. This way the negative effects of impurities or damages in the elastomeric bodies are minimized.
Corrugations of the kind as illustrated in US 2004/0012301 and WO 03/056287 is very suitable for anisotropic purposes where a change in the electrostatic force between the two electrodes by compression prolongs the body in essentially one planar direction given by the parallel extension of the corrugations.
Furthermore, the known dielectric transducer structures sometimes suffer from broken electrodes because part of the mechanical forces will always work in the non-compliant direction of the structure. In the non-compliant direction, the electrodes are flat and thus the elasticity of the structure is mainly limited by the typically high elastic modulus of electrode materials, for example metals. If the strains in this direction become too large, the electrode will thus break.
New applications of dielectric transducer structures now ask for a compliance to elastic deformations in both planar directions of the boundary surfaces, or more preferable in all planar directions in the two plane level.
One document WO 01/06579 discloses an electroactive polymer including a roughened surface having random texturing, where this roughened surface allows for planar deflection that is not directionally compliant. Such a random texturing however also implies loss in the control of the transducer performance.
The solution is to introduce an ‘egg tray’ kind of surface structure, it has however been found that not any such structure will have sufficient compliance in all planar directions, the risk is especially for non-randomized but more regular surface structures, where there is a risk that ‘straight lines’ may appear at the surface topology. Such straight lines are sections where the surface topology is basically flat and extend along some line or sections of a direction in the plane, along such lines the compliance is low and there is risk of electrode damage when the polymer is stretched.